High frequency system



June 30, 1936. N. P. yCASE 2,045,569

HIGHv FREQUENCY SYSTEM Filed Alril 25, 1934 s sheets-sheet 1 INVETOR ma 50N P m55 BY r EN, E. 'MEW ArroRNl-:Ys

Ju'ne 3Q, 1936.," 1-

N. P. cAsE 2,045,569

HIGH FREQUENCY sYsTEM i Filed April 25,'l 19:54 3 sheets-sheet 2 June 30, 1936. N. P. cAsE HIGH FREQUENCY SYSTEM Filed April 25, 1934 3 Sheets-Sheet 3 lmwam'on E L Cffm P.,N R Lo 0 5 l a ND Vial B Patented June l30, 1.936 v t UNITED STATES PATENT OFFICE 2,045,569 man FREQUENCY SYSTEM Nelson P. Case, Bayside, N. Y., assigner to Hazeltine Corporation, Jersey City, N. J., a corporation of'Delaware Application April 25, 1934, Serial No. 722,313

' broadcast receiving systems.

'I'he invention is particularly applicable to so` called all wave receivers operative over a frequency range considerably in excess ofthe present broadcast band of 550 to 1500 kllocycles. An object oi the invention is to secure an over-all gain which remains substantially constant throughout the entire all wave" range of the receiver.

In a heterodyne system, the conversion gain is determined in large. measure by the performance of the heterodyne oscillator. Conversion gain is deilned as the ratio of the modulated signal voltage at the output of the modulator to the reception frequency signal voltage at the input of the modulator. If the oscillation amplitude of the heterodyne source decreases, as is usually the case at extremely high frequencies, the amplitude of the modulated signal, and hence the conversion gain, will likewise decrease.

It is proposed in accordance with the' present invention to compensate or minimize variations in intensity of the modulated signals otherwise resulting from such changes in oscillation amplitude, by utilizing a biasing voltage derived from the heterodyne oscillations, and automatically to control the amplification or gain of the receiving system in inverse relation to the oscillation amplitude, so that as the oscillation amplitude decreases the gain will be automatically increased tsmaintain'the over-ali gain substantially constant.

A biasing voltage varying with the oscillation amplitude is conveniently secured by associating a blocking condenser-leak resistance combination with a grid of the oscillator. 'I'he biasing voltage thus derived may be applied to the control electrodes of one or more of the reception frequency or modulatedfrequency ampliiler tubes to adjust the signal ampliilcation inversely to the amplitude of oscillations.

Alternatively'the modulating element of the system may be rendered regenerative, as by regeneratively coupling its input and output circuits,

and the oscillator grid biasing voltage applied to the modulator to control the regenerative gain. If. with this modification, `separate tubes are employed for the oscillator and modulator, the biasing voltage is Vapplied to tl1e-modulator control grid. In the case of a single multi-grid tube, such r las a hexode, serving as acombined oscillatormodulator, wherein oscillations are produced by the inner triode section including the cathode, and

A12 claim.. (c1. 25o-zo) modulation effected by` the outer tetrode section including the anode, a virtual cathode is established between oscillator and modulator portions, the emission of which, is automatically regulated inversely lto the biasing voltage established on the l oscillator grid. lThe mutual conductance of the outer tetrode section. and hence the regenerative gain, varies with th Iemission f the virtual cathode.

With any of the mentioned modiilcations, when the oscillation amplitude is large, the average negative bias derived from the oscillator, islikewise large. This produces a relatively low mutual conductance in the biased amplifier or modulator elements, resulting in a small gain of the signals. Conversely when the oscillation amplitude is small, th'e negative biasing voltage is likewise small, and the mutual conductance of the biased elements correspondingly high, giving greatly increased gain. By suitably proportioning the circuit components, in the manner described below, the change in ampliiication may be caused to compensate to a desired extent for variations in the oscillation amplitude, and such preferably as to maintain the over-all gain substantially constant throughout a considerable range vof variation in' oscillation amplitude. In the drawings:

- Figure 1 is a circuit diagram of a superheterodyne receiving system employing the invention, wherein a single multi-grid tube functions as a combined oscillator and regenerative modulator. Figure 2 shows diagrammatically the oscillatormodulator portion of a system, such as that of Fig. l', but modified to employ separate oscillator and modulator tubes.

Figures 3 and 4 are comparative performance graphs illustrating lthe conversion gain and the amount of regeneration present for various oscillation amplitudes and regenerative couplings in systems such as those of Figures 1 and 2.

Figure-5 shows diagrammatically the oscillatormodulator and ilrst stage of modulation fretube Va, followed by a combined detector and 2 stage of a-f amplification, tube V4, and a stage of audio-frequency amplification, tube Vs, the output of which is applied to a loud speaker L. The system is energized from the usual rectifierlter combination B, for converting the house supply of alternating current into substantially non-pulsating uni-directional voltage applied to the voltage distributing resistors D. The manner of supplying voltages to the individual tubes over conductors such as E, is obvious from the drawings and requires no detailed discussion.

High-frequency signals are supplied to the' system from an antenna circuit I coupled to the input of tube V1 through a transformer T1, comprising a primary coil P1 and a secondary coil S1 tuned by a variable condenser C1. similar tuned transformer coupling Tn, C2 is employed between tubes V1 and V2. The secondary coil S1 of transformer T1, together with the primary Pz and secondary S2 coils of transformer T2 are tapped at intermediate points to contacts of rotary switches R1, Rz and Ra, respectively, for adjusting the system to operate over successive frequency bands of the all wave range. The rotary switch arms are ganged to a unitary control U1 to provide'simultaneous band adjustments of all circuit components. Likewise the tuning condensers C1 and Ca are ganged to a unitary control Un for simultaneously tuning the circuits by continuous gradation throughout each frequency band. Certain portions of coils S1 and S2 are individually shunted to ground by semiadjustable padding condensers such as C4 and C5 as a means of aligning the tuned circuits.

Tubes V2, V3 and V4 are coupled in cascade by means of transformers Ts and Ts tuned to the intermediate frequency by means of semi-adjustable condensers C5 and Ca arranged in shunt to the transformer windings. The circuit connections for the detector V4, audio-frequency amplifier V5, and loud speaker L are apparent from the drawings.

The oscillator-modulator tube Va contains within its single glass receptacle: a cathode K,

anv anode A, and a plurality of grids successively disposed therebetween, which may, for purposes of this disclosure, be designated as an inner. oscillator grid 4, an oscillator anode grid 5, an inner screen 6, the signal control grid 1, and an outer screen B.

For impressing upon the oscillator-modulator, tube Va, high-frequency signals impinging on the antenna circuit I, the secondary coil Sz, of transformer Tnhas its high-potential terminal connected to the signal control grid 1, the low-potential end of coil Sn being grounded at high frequencies through the by-pass condenser 9. The

cathode K of t'ube Vn is effectively grounded at the reception and heterodyne frequencies through the by-pass condenser C1 shunting the .biasing resistor I0.

I 7 The inner triode section of K and grids 4 and 5, is adapted tube Va comprising the cathode by means of the associated impedances external to the tube, to generate oscillations of heterodyne frequency. Thus the grids land 5 are connected respectively through magnetically coupled coils P4 and Ps to ground at I5. The cathode K is likewise, as stated, effectively grounded at the heterodyne frequency through the by-pass condenser Cv. The circuits thus traced from grids I and 5 through ground tothe cathode K, are regeneratively coupled by virtue of the etic coupling between coils P4 and Ps. which are p erlypoledtothisend. This 1 l A somewhat is such as to establish and maintain sustained oscillations throughout the all wave operating range of the system. The frequency of oscilla-l 'of switches R1. Rz and R3. Padding condensers such as Ca and C10, are associated with individual tapped portions of coil P5 for purposes of aligning the several tuned circuits for actuation by the unitary control U2 mechanically coupled to condenser Co as well as to condensers C1 and C2.

Coils P4 and P5 are largely responsible for variations in the amplitude of heterodyne oscillations with frequency change. Within a given frequency band, the oscillation amplitude increases with frequency in consequence of the increase in self and mutual impedances of coils P4. and P5. Also as the operating range is adjusted from a frequency band of lower to one of higher order, the average amplitude of oscillation will in general decrease, due to the decreasing self and mutual impedances of coils P4 and P5, which results from tapping to successively smaller portions thereof.

Alterations in the oscillation amplitude produced by these and other factors are, in accordance with the present invention, compensated for in the mannerstated, by regeneratively am plifying the modulated signals in the outer tetrode section of the tube, which includes the signal control grid I and the anode A, and causing -the extent of this regenerative amplification to be varied in inverse relation to change in the oscillation amplitude.

This regenerative energy transfer is accomplished by connecting the intermediate-frequency tuning condenser C11, from the anodeA, directly to the cathode K. The cathode K is, at the modulated or intermediate frequency, maintained considerably above ground potential by the impedance of condenser C1. The signal control grid 1, however, is, at the intermediate frequency, effectively grounded through coil Sa and by-pass condenser 9, which have relatively small impedances at this frequency. Accordingly, at the intermediate frequency, the anode A and the control Agrid I assume opposite instantaneous alternating current polarities with respect to the cathode K, which is the requisite condition for regenerative feedback.

The percentage of energy thus regeneratively transferred from the anode circuit to the signal control grid circuit ofA tube V2, is determined by l tial on grid l likewise decreases, in com1 amplitude decreases, the average negative bias- In this way the energy regeneratively transferred at the intermediate frequency from the output circuit associated with anode A to the input circuit associated with the control grid 1. is caused to vary inversely with the amplitude oi.' oscillation. By suitably proportioning the capacity oi condenser C7 in relation to that of condenser Cn, the conversion gain of tube V2 between its input and output circuits, may be caused to remain reasonably independent of variations in the oscillator amplitude .throughout the entire all wave range of the system.

Fig. 2 illustrates the invention as applied to a system employing separate modulator Vs and oscillator V1 tubes.V Incoming signals are applied through transformer T2, having a secondary Sz, tuned by C2 to the reception frequency, to the signal control grid Ge of the modulator, the modulated output being relayed to the remainder of the system through the tuned transformer Ts. The modulated output 'is regeneratively amplified in tube Ve by virtue of ,the condensers C11 and C1 effectively connected between the anode Ae and the cathode Ke, and between the grid Ge and the cathode, respectively.

In the oscillator circuit, a .tuned impedance consisting of coil P4 shunted by variable condenser Co, is connected between grid G1 and the grounded cathode K1, of tube V7. The 'anode A1 is grounded through a coil P5 and a by-pass condenser I6.

vCoil P5 is so coupled magnetically to coil P4, as

to produce sustained oscillations of a frequency determined by the settingi of condenser C9. The oscillations are applied between ground and the cathode of the modulator tube Vs, over a. connection I1, which includes a coil Pe magnetically coupled to coils P4 and P5. I

The blocking condenser C12, in series with the grid G1 of tube V1, and the leak resistance R between grid and cathode of tube Vv, provide a. biasing voltage derived from the oscillation amplitude, which is applied over a connection I8 to the signal control grid Ga of the modulator.

1 This connection includes series resistances R2 and Ra, the intermediate point of which is grounded through a by-pass condenser C15, for filtering out pulsating componentsof the biasing voltage.

In the operation of the Fig. 2 circuit, the increased bias on the oscillator grid resulting from an increase in oscillation amplitude, is applied over conductor I8 to the modulator gridfthereby decreasing the 'modulator mutual conductance and with it the regenerative amplification of the modulated signals. The converse of this chain of reactions is produced by-adecrease in the oscillation amplitude. v

Fig. 3 illustrates by means of comparative graphs the eil'ect on the conversion gain of-altering the capacity of condenser Cv, condenser Cn remaining fixed except for the necessary retuning. selecting a value K for this condenser affords a reasonably constant conversion gain for .wide variations lin the oscillation` amplitude of the order of one to eight volts. It will be apparent from the graphs that the adjustmentof condenser C1 is.- however, fairly critical, and should not vary by more than say plus or minus ten percent froml thev value K. If a capacity of approximately .8 K is employed, the regeneration tends to produce oscillations for small amplitudes of the heterodyne oscillator.- On the other hand, if the capacity K is doubled, the conversion gain falls'oil' version gain for the condition that the regenerative coupling is omitted.

Fig. 4 shows for the C1 capacity values of Fig. 3, the amount of regenerative amplification provided by the modulator for various amplitudes of heterodyne oscillations.

Fig. 5 illustrates the invention as applied to s. system employing a multi-grid tube, Va, as u. combined oscillator and non-regenerative modulator, the gain control being applied to the modulation frequency amplifier tube, V3. Incoming signals are applied through transformer T2, having a secondary S2, tuned by C2 to the reception frequency, to the signal control grid I of the modulator section of tube Vs, the modulated output being relayed to the modulation frequency amplifier tube Vs through the tuned transformer T5. I In the oscillator circuit, a tuned impedance consisting of coil P4 shunted by variable condenser Cs is connected 'between grid l and cathode K of tube Va, through the by-pass condenser C1. The-oscillator anode grid 5, is likewise ccnnected to the cathode K, through condenser I6, coil Ps, an d by-pass condenser Cv. Coil P5 is so coupled magnetically to coil-Peas to produce sustained oscillations of a frequency determined by the setting of condenser Cor 'I'he oscillations serve to produce modulation of the signals applied to control grid 1 by virtue of their effect of varying the emission of the virtual cathode which exists between the innerscreen 6 and the signal control grid l.

For low amplitudes of oscillation, the conversion gain of the tube Va'varies directly with the oscillation amplitude. v

'I'he blocking condenser C11, in series with the grid 4 of tube Vs, and the leak resistance R between grid 4 and cathode K of tube Vs. provide a biasing voltage derived from the oscillation amplitude, which .is appliedover a connection I8 to the signal control grid 22 of the modulation frequency amplifier tube Va. This connection includes series resistances Ra and R3, and bypass condensers C15 and C21, for ltering out -the modulation frequency amplifier tube Va and with it the amplification. of the modulated signals secured by means o! tube 'Va The converse of this chain of reactions is produced by a decrease in the oscillation amplitude.

I claim: l

-1. In a heterodyne signaling system, a vacuum tube modulator, a source of heterodyne oscillations for modulating signals. said oscillations being subject to undesired changes in amplitude, and means .reducing the eil'ects of said changes on intensity oi' thev modulated signals comprising, means rendering said modulator' regenerative to modulated slgnalsLand means responsive to saidsource for varying the regeneration of said modulator inverselyto said changes in oscillation amplitude.

2. In a heterodyne signaling system, a vacuum tube modulator, a source of heterodyne oscillations for modulating signals, said oscillations being subject to undesired changes in amplitude, and means minimizing the effects of said changes on intensity of the modulated signals comprising, means rendering said modulator regenerative to said modulated signals, and means responsive to said heterodyne oscillations for Varying the regeneration of said modulator inversely to said changes in oscillation amplitude.

3. In a heterodyne signaling system, a vacuum tube modulator, a. source of heterodynev oscillations for modulating signals, said oscillations being subject to undesiredpchanges in amplitude, and means substantially compensating the effects of said changes in oscillation amplitude on intensity of themodulated signals comprising, means rendering said modulator regenerative to modulated signals, and means responsive to said heterodyne oscillations for so adjusting the regeneration of said modulator inversely to said changes in oscillation amplitude as substantially to counterbalance the eilects of said changes in oscillation amplitude on the modulated signals.

4. In a heterodyne receiving system, a vacuum tube modulator, a source of heterodyne oscillations for modulating signals, said oscillations being subject to undesired changes in amplitude, and means reducing the effects of said changes on intensity of the modulated signals comprising, means rendering said modulator regenerative to modulated signals, and means responsive to said heterodyne oscillations for varying, in inverse relation to the amplitude of said oscillations, the mutual conductance of said modulator and thereby the extent or its regeneration.

5. lIn a superheterodyne radio receiving system, a vacuum tube modulator, a source of heterodyne oscillations for modulating signals, said oscillations being subject to undesired changes in amplitude, and means reducing the effects of said changes on .the intensity of the intermediate frequency signals comprising, means rendering said modulator regenerative to intermediate frequencies, and means responsive to said heterodyne oscillations for varying the regeneration of said modulator inversely to said changes in oscillation amplitude.

6. In a heterodyne signaling system, a multigrid vacuum tube consisting of an inner section including a pair of grids and a cathode, and an outer section including a signal control grid and an anode, means adapting said inner section to generate heterodyne oscillations, means adapting said outer section to modulate signals therewith, said heterodyne oscillations being subject to undesired changes in amplitude, and means reducing the eilects of said4 changes on intensity of the modulated signals comprising, means rendering said outer section regenerative to modulated signals, and means applying to a grid of .said inner section a negative biasing potential derived from said heterodyne oscillations for varying the modulated signal regeneration inversely to said changes in oscillation amplitude.

7. In a heterodyne signaling system, a multigrid vacuum tube consisting of an inner section including a pair of grids and a cathode, and an outer section including a signal control grid and an anode, means adapting saidy inner section to generate heterodyne oscillations, means adapting said outer section to modulate signals therewith, said heterodyne oscillations being subject to undesired changes in oscillation amplitude, and means reducing the effects of said changes on intensity of the modulated signals comprising, means rendering said outer section regenerative to modulated signals, and a grid-leak associated with a grid of said inner section for varying the mutual conductance and thereby the regeneration of the outer section inversely to said changes in oscillation amplitude.

, 8. In a heterodyne receiving system an oscillator-modulator comprising a vacuum tube having successively disposed between a cathode and an anode thereof, an inner grid., an oscillator anode grid, anda control grid responsive to signals, means reactively coupling said inner and oscillator anode grids to said cathode to produce heterodyne oscillations for modulating signals, said oscillations being subject to undesired changes in amplitude, and means reducing the effects of said changes on intensity of the modulated signals comprising, a regenerative coupling between said anode and control grid for regeneratively amplifying the modulated signals, and means applying to said inner grid a negative biasing voltage derived from said heterodyne oscillations.

9. In a heterodyne receiving system an oscillator-modulator comprising, a vacuum tube having successively disposed between a cathode and an anode thereof, an inner grid, an oscillator anode grid, and a control grid responsive to signals, means reactively coupling said inner and oscillator anode grids to said cathode to produce heterodyne oscillations for modulating signals, said oscillations being subject to undesired changes in amplitude, and means reducing the effects of said changes on intensity of the modulated signals comprising, a regenerative coupling between said anode and control grid for regeneratively amplifying the modulated signals, and a grid-leak associated with said inner grid for applying thereto a negative biasing voltage derived from said heterodyne oscillations.

l0. In a heterodyne signaling system, a vacuum tube modulator having ari-anode, a cathode and a control grid, a source of heterodyne oscillations subject to variations in amplitude, and means reducing the eiects of said variations on the modulated signals comprising, a regenerative coupling for said modulator selectively responsive to the modulated signals, said coupling including a pair of capacities effectively connected between said anode and cathode and between said cathode and grid respectively, the ratio of said capacities determining the extent of said regeneration, and means deriving a biasing voltage from said source of heterodyne oscillations for varying said regeneration inversely to changes in the oscillation amplitude.

11. In a heterodyne signaling system, a vacuum tube modulator having an anode, a cathode and a control grid, a source of heterodyne oscillations subject to variations in amplitude, and means reducing the effects of said variations on the modulated signals comprising, aregenerative coupling for said modulator selectively responsive to the modulated signals, said coupling including a pair of capacities effectively connected between said anode and cathode and between said cathode and grid-respectively, the ratio of said capacities determining the extent of said regeneration, and

means deriving a biasing voltage from said source of heterodyne oscillations for varying said regeneration inversely to changes in the oscillaamiamol y 5 constant for relatively wide variations in theoscillation amplitude.

12. In a heterodyne signaling system including a signal modulator and a source of heterodyne 5 oscillations subject to variations in amplitude,

the method oi' compensating e'ects of said variations on the modulated signals which comprises,

regeneratively amplifying the modulated signals, deriving from said heterodyne oscillations4 a biasing voltagel varying with the amplitude thereof, and utilizing said biasing voltage to regulate the regenerative ampliilcation inversely to the oscillation amplitude.

NELSON P; CASE.` 

